Diffusion weighted magnetic resonance imaging is a known prior art technique. In diffusion weighted magnetic resonance imaging the diffusion tensor is obtained from, the magnetic resonance measurement signal for a defined body region of interest. The diffusion tensor is then visualised by known imaging methods (U.S. Pat. No. 5,539,310; La Bilhan et al, Diffusion Tensor Imaging: Concepts and Applications, Journal of Medical Resonance Imaging 13:534-46 (2001); Lawrence R. Frank, Anisotropy in High Angular Resolution Diffusion-Weighted MRI, Magnetic Resonance in Medicine 45:935-939 (2001),). An overview of known diffusion-weighted magnetic resonance techniques is provided by Gray L. MacFall J. Overview of diffusion Imaging. Magnetic Resonance Imaging Clin N Am 1998; 6:125-138.
In addition in vivo intravoxel incoherent motion (IVIM) magnetic resonance imaging is a known technique (La Bilhan D et al, MR imaging of intravoxel inchoherent motions: application to diffusion and perfusion in neurological disorders. Radiology 1986:161:401-407.) In particular, the interpretation of IVIM measurements with respect to classical perfusion has been discussed in the prior art (La Bilhan D et al., Separation of diffusion and perfusion in intravoxel incoherent motion MR Imaging. Radiology 1998:168:497-505; Henkelman R M. Does IVIM measure classical perfusion? Magn Reson Med 1990:16:470-475; Le Bilhan D, Turner R. The capillary network: a link between IVIM and classical perfusion. Magn Reson Med Med 1992:27:171-178). This imaging technique uses gradient encodings for random motion.
Classical perfusion is a measure of the blood delivered to and used by a specified mass of tissue. It is often measured using spin labelling techniques in MRI. In contrast, IVIM measures quasi-random blood movement within a single imaging voxel and results in a bi-exponential signal attenuation in a standard pulsed gradient spin echo (PGSE) experiment (cf. R. J. Moore et al, in vivo intravoxel incoherent motion measurements in the human placenta using echo-planar imaging at 0.5 T, Magnetic Resonance in Medicine, 43;295-302 (2000)).
It is a common disadvantage of prior measurement techniques that only a scalar value for the perfusion is obtained even though perfusion usually is anisotropic. A scalar perfusion value therefore only gives a limited amount of information on the actual nature of the perfusion.
Therefore the present invention aims to provide an improved imaging method which enables imaging and visualisation of the perfusion anisotropy as well as a corresponding computer program product and perfusion imaging apparatus.